The precise positioning of rocker lever assemblies on an internal combustion engine is important both to the life of the rocker lever and the operation of the associated valves, fuel injectors and other structures. In addition, proper support for internal combustion engine rocker lever assemblies is essential if the rapid movement of the rocker levers and associated structures during engine operation is to be sustained. Provision of the desired alignment and necessary support for the rocker levers may be further complicated by the configuration of the engine cylinder head. Engine designs which employ four valves for each cylinder rather than the more commonly encountered two valves also present design challenges for the operative support of the rocker levers associated with these valves. Some engine designs require rocker lever support structures with complex shapes to locate the rocker levers in positions which will mesh with pushrods or other connecting elements. The shapes of such rocker lever supports may be sufficiently complex that they are extremely expensive to machine.
An engine which employs four valves for each cylinder must accommodate the rocker levers and supporting structure in a relatively limited area. Mounting each rocker lever on a single support provides more flexibility than mounting a pair of rocker levers on a single support.
The prior art has proposed rocker lever assemblies for internal combustion engines. U.S. Pat. No. 4,655,177 to Wells et at., for example, which is commonly owned by the assignee of the present invention, describes a rocker arm or lever support assembly. This support assembly includes a pedestal which mounts a pair of rocker levers on a single shaft. The lateral spacing between the rocker levers is chosen to conform to the locations of the pushrods and valve stems which engage the ends of each rocker lever. This rocker lever support arrangement is well suited to an engine configuration which employs only two valves for each cylinder. However, it will not work effectively with an engine configuration that requires both four valves per cylinder and the locations of the rocker lever ends to mesh with existing parts.
U.S. Pat. No. 4,732,119 to Melde-Tuczai et al. discloses rocker lever supports for an internal combustion engine with two or more valves per cylinder. Each rocker lever is individually mounted on a separate support structure. However, these rocker levers are directly actuated by contact with cams on a rotating camshaft, which presents drastically different engine design considerations from optimally positioning and mounting rocker levers on the cylinder head to actuate four valves per cylinder in a compression ignition engine.
U.S. Pat. No. 4,721,075 to Kasai discloses individually mounted rocker lever supports for a two valve engine configuration.
Norwegian Patent No. 79167 to Pielstick discloses a rocker lever support assembly that mounts and supports rocker levers capable of actuating four valves. However, this complex arrangement, which would be expensive to manufacture, mounts two parallel rocker levers on a single shaft and a third rocker modified to actuate two valves on a separate shaft. This arrangement, moreover, fails to provide a low cost solution to the optimal location and support for the rocker levers required to actuate four valves in each engine cylinder.
The prior art, therefore, has failed to provide a simple, low cost rocker lever support assembly that can be mounted on an engine cylinder head so that the rocker lever assembly components are capable of meshing with existing engine parts to optimally position and support the rocker levers required to actuate four valves for each engine cylinder. A need exists for such a rocker lever support assembly.